<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        /*
            比较运算符
                &&
                ||
                ！

         */
        var str;
        document.write((!!0) +"<br>");
        document.write((!!1) +"<br>");
        document.write((!!str) +"<br>");


        //三元运算符


        var a = 3 < 4 ? 1 : 0;
        document.write(a)

    </script>
</head>
<body>

</body>
</html>